The README file which comes with every LedgerSMB software release should be considered the canonical source for system requirements. In summary, the following technical components are required:
A web server (known working are Nginx, Apache, lighttpd and Varnish)
Modern Perl 5, with additional modules
PostgreSQL 13 or higher
(optional) LaTeX or XeLaTeX from the TeTeX or TeXLive TeX distributions
More information about system requirements for clients and servers is available at https://ledgersmb.org/content/system-requirements.
System requirements such as required RAM and number of CPUs and their speed largely depend on the expected system activity. However, any modern VPS should provide enough memory and storage to satisfy a reasonable number of users.